New roof sheathing over old?
New roof sheathing over old?
(OP)
50 year-old house with 3/8" plywood sheathing on trusses spaced at 24". Roof shingles are to be replaced. Attic ventilation comprises of a poorly installed ridge vent with no soffit vents. Walking on the roof feels very "spongy". There does not appear to be any roof leaks but, from poking at the sheathing from below, there appears to be "dry" rot.
My first thought was to replace the sheathing with 5/8" plywood. Any opinions on if 3/8" sheathing could just be applied over the existing sheathing, eliminating the removal? The ventilation issues will be addressed with proper soffit and ridge vents.
My first thought was to replace the sheathing with 5/8" plywood. Any opinions on if 3/8" sheathing could just be applied over the existing sheathing, eliminating the removal? The ventilation issues will be addressed with proper soffit and ridge vents.






RE: New roof sheathing over old?
The new sheathing needs to function as a diaphragm and you're going to be attaching it through rotting material into the supports. Have you checked that the trusses themselves aren't presenting signs of deterioration? I don't know of any provision that prohibits it, but it seems like a poor decision.
RE: New roof sheathing over old?
As far as thickness, what does your local code say? Personally, I like something thicker. I would expect any 3/8" plywood to feel "spongy" when walked upon.
In my climate I would also use "solarboard" for any significant replacement, to reduce attic temperature. Might actually be worth just redoing all the sheathing for the energy savings from the solarboard - depending on how much is rotted. My local Home Depot keeps it in stock. Solarboard has a low-emissivity (foil) facing which goes on the attic side.
http://www.norbord.com/na/roof-sheathing/solarbord...
Also, are you using EnergyStar shingles? This will reduce roof and attic temperature. If you pick the right vendor, the cost is about the same as normal shingles (some roofers will try to rip you off and charge an extra couple thousand for the EnergyStar shingles)
You may be able to get tax credits for the solarboard and/or EnergyStar shingles. You will have to investigate current rules yourself - I know I got back a $1,500 federal tax credit for using EnergyStar shingles a few years ago, and I picked a roofer who charged the same for the EnergyStar or normal shingles. The rules change all the darn time, though. Looks like the current credit is $500 (10% of material cost) only, whereas mine was 30% of the overall cost, capped at $1,500. There may be local incentives as well.
http://energystar.supportportal.com/link/portal/23...
RE: New roof sheathing over old?
RE: New roof sheathing over old?
Mike McCann
MMC Engineering
RE: New roof sheathing over old?
RE: New roof sheathing over old?
RE: New roof sheathing over old?
Mike McCann
MMC Engineering
RE: New roof sheathing over old?